Considering its vast size, Africa has few extensive mountain ranges and fewer high peaks than any other continent. The major ranges are the Atlas Mountains along the northwest coast and the Cape ranges in South Africa. Lowland plains are also less common than on other continents.
Geologists characterize Africa's topography as an assemblage of swells and basins. Swells are rock strata warped upward by heat and pressure while basins are masses of lower lying crustal surfaces between swells. The swells are highest in East and central West Africa where they are capped by volcanic flows originating from the seismically active East African rift system. The continent can be visualized as an uneven tilted plateau, one that slants down toward the north and east from higher elevations in the east and south.
During much of the Cretaceous period, from 130 million to 65 million years ago, when dinosaurs like tyrannosaurus, brontosaurus, and triceratops walked the earth, Africa's coastal areas and most of the Sahara Desert were submerged underwater. Global warming during the Cretaceous period melted polar ice and caused ocean levels to rise. Oceanic organic sediments from this period were transformed into the petroleum and natural gas deposits now exploited by Libya, Algeria, Nigeria and Gabon. Today, oil and natural gas drilling is conducted both on land and offshore on the continental shelf.
The continent's considerable geological age has allowed more than enough time for widespread and repeated erosion, yielding soils leached of organic nutrients but rich in iron and aluminum oxides. Such soils are high in mineral deposits such as bauxite (aluminum ore), manganese, iron, and gold, but they are very poor for agriculture. Nutrient-poor soil, along with deforestation and desertification (expansion of deserts) are just some of the daunting challenges facing African agriculture in modern times.
Science EncyclopediaScience & Philosophy: Adrenoceptor (adrenoreceptor; adrenergic receptor) to AmbientAfrica - Origin Of Africa, Continental Drift, General Features, East African Rift System, Human Evolution